Four-wheel drive (4WD) vehicles are four-wheeled vehicles with a drivetrain that may be controlled to allow all four wheels to receive torque from the engine at the same time. Four-wheel drive vehicles are typically placed from a two-wheel drive mode, where torque is only applied to two of the wheels, to the four-wheel drive mode by the driver when more traction is desired. Currently, the term all-wheel drive (AWD) is used to refer to a vehicle that operates in a four-wheel drive mode “full time” without the need for the driver to activate the four-wheel drive mode. Four-wheel drive vehicles are also known or advertised as four-by-four (4×4) vehicles.
When switched into four-wheel drive mode, the vehicle's transfer case will lock the front-axle driveshaft to the rear-axle driveshaft, forcing the wheels to spin at the same speed. Some transfer cases also contain an additional set of gears providing the vehicle with a low range four-wheel drive mode (4-LO). The low range gear ratio gives the vehicle extra torque and a slow output speed, which allows drivers to slowly and smoothly crawl up very steep hills and dunes, or drive over rocky terrain.
The low range mode works well for climbing and descending hills and dunes. Problems may arise for manual four-wheel drive vehicles, however, if the driver decides to coast down the hill or dune while depressing the clutch pedal when the vehicle is in the low range mode and still in gear. This situation will lead to excessive spinning of the clutch disk (e.g., almost two-times its specified rate), often referred to as over-speeding the clutch, which could cause the clutch to burst. Compounding the issue is the fact that the clutch over-speed condition may occur at low speeds and often times the driver may not even be aware of the potential problem. Repairing or replacing a burst clutch can be expensive and could cause the vehicle manufacturer to lose goodwill with the driver (even though it is the driver's actions that necessitated the repairs).
Accordingly, there is a need and desire to detect when driving and operating conditions are detrimental to the vehicle's clutch in a four-wheel drive manual transmission vehicle and to implement countermeasures to avoid damage to the clutch.